# $Id: crc32c.py 23 2006-11-08 15:45:33Z dugsong $
# -*- coding: utf-8 -*-
from __future__ import absolute_import

import array

# CRC-32C Checksum for SCTP
# http://tools.ietf.org/html/rfc3309

crc32c_table = (
    0x00000000, 0xF26B8303, 0xE13B70F7, 0x1350F3F4, 0xC79A971F,
    0x35F1141C, 0x26A1E7E8, 0xD4CA64EB, 0x8AD958CF, 0x78B2DBCC,
    0x6BE22838, 0x9989AB3B, 0x4D43CFD0, 0xBF284CD3, 0xAC78BF27,
    0x5E133C24, 0x105EC76F, 0xE235446C, 0xF165B798, 0x030E349B,
    0xD7C45070, 0x25AFD373, 0x36FF2087, 0xC494A384, 0x9A879FA0,
    0x68EC1CA3, 0x7BBCEF57, 0x89D76C54, 0x5D1D08BF, 0xAF768BBC,
    0xBC267848, 0x4E4DFB4B, 0x20BD8EDE, 0xD2D60DDD, 0xC186FE29,
    0x33ED7D2A, 0xE72719C1, 0x154C9AC2, 0x061C6936, 0xF477EA35,
    0xAA64D611, 0x580F5512, 0x4B5FA6E6, 0xB93425E5, 0x6DFE410E,
    0x9F95C20D, 0x8CC531F9, 0x7EAEB2FA, 0x30E349B1, 0xC288CAB2,
    0xD1D83946, 0x23B3BA45, 0xF779DEAE, 0x05125DAD, 0x1642AE59,
    0xE4292D5A, 0xBA3A117E, 0x4851927D, 0x5B016189, 0xA96AE28A,
    0x7DA08661, 0x8FCB0562, 0x9C9BF696, 0x6EF07595, 0x417B1DBC,
    0xB3109EBF, 0xA0406D4B, 0x522BEE48, 0x86E18AA3, 0x748A09A0,
    0x67DAFA54, 0x95B17957, 0xCBA24573, 0x39C9C670, 0x2A993584,
    0xD8F2B687, 0x0C38D26C, 0xFE53516F, 0xED03A29B, 0x1F682198,
    0x5125DAD3, 0xA34E59D0, 0xB01EAA24, 0x42752927, 0x96BF4DCC,
    0x64D4CECF, 0x77843D3B, 0x85EFBE38, 0xDBFC821C, 0x2997011F,
    0x3AC7F2EB, 0xC8AC71E8, 0x1C661503, 0xEE0D9600, 0xFD5D65F4,
    0x0F36E6F7, 0x61C69362, 0x93AD1061, 0x80FDE395, 0x72966096,
    0xA65C047D, 0x5437877E, 0x4767748A, 0xB50CF789, 0xEB1FCBAD,
    0x197448AE, 0x0A24BB5A, 0xF84F3859, 0x2C855CB2, 0xDEEEDFB1,
    0xCDBE2C45, 0x3FD5AF46, 0x7198540D, 0x83F3D70E, 0x90A324FA,
    0x62C8A7F9, 0xB602C312, 0x44694011, 0x5739B3E5, 0xA55230E6,
    0xFB410CC2, 0x092A8FC1, 0x1A7A7C35, 0xE811FF36, 0x3CDB9BDD,
    0xCEB018DE, 0xDDE0EB2A, 0x2F8B6829, 0x82F63B78, 0x709DB87B,
    0x63CD4B8F, 0x91A6C88C, 0x456CAC67, 0xB7072F64, 0xA457DC90,
    0x563C5F93, 0x082F63B7, 0xFA44E0B4, 0xE9141340, 0x1B7F9043,
    0xCFB5F4A8, 0x3DDE77AB, 0x2E8E845F, 0xDCE5075C, 0x92A8FC17,
    0x60C37F14, 0x73938CE0, 0x81F80FE3, 0x55326B08, 0xA759E80B,
    0xB4091BFF, 0x466298FC, 0x1871A4D8, 0xEA1A27DB, 0xF94AD42F,
    0x0B21572C, 0xDFEB33C7, 0x2D80B0C4, 0x3ED04330, 0xCCBBC033,
    0xA24BB5A6, 0x502036A5, 0x4370C551, 0xB11B4652, 0x65D122B9,
    0x97BAA1BA, 0x84EA524E, 0x7681D14D, 0x2892ED69, 0xDAF96E6A,
    0xC9A99D9E, 0x3BC21E9D, 0xEF087A76, 0x1D63F975, 0x0E330A81,
    0xFC588982, 0xB21572C9, 0x407EF1CA, 0x532E023E, 0xA145813D,
    0x758FE5D6, 0x87E466D5, 0x94B49521, 0x66DF1622, 0x38CC2A06,
    0xCAA7A905, 0xD9F75AF1, 0x2B9CD9F2, 0xFF56BD19, 0x0D3D3E1A,
    0x1E6DCDEE, 0xEC064EED, 0xC38D26C4, 0x31E6A5C7, 0x22B65633,
    0xD0DDD530, 0x0417B1DB, 0xF67C32D8, 0xE52CC12C, 0x1747422F,
    0x49547E0B, 0xBB3FFD08, 0xA86F0EFC, 0x5A048DFF, 0x8ECEE914,
    0x7CA56A17, 0x6FF599E3, 0x9D9E1AE0, 0xD3D3E1AB, 0x21B862A8,
    0x32E8915C, 0xC083125F, 0x144976B4, 0xE622F5B7, 0xF5720643,
    0x07198540, 0x590AB964, 0xAB613A67, 0xB831C993, 0x4A5A4A90,
    0x9E902E7B, 0x6CFBAD78, 0x7FAB5E8C, 0x8DC0DD8F, 0xE330A81A,
    0x115B2B19, 0x020BD8ED, 0xF0605BEE, 0x24AA3F05, 0xD6C1BC06,
    0xC5914FF2, 0x37FACCF1, 0x69E9F0D5, 0x9B8273D6, 0x88D28022,
    0x7AB90321, 0xAE7367CA, 0x5C18E4C9, 0x4F48173D, 0xBD23943E,
    0xF36E6F75, 0x0105EC76, 0x12551F82, 0xE03E9C81, 0x34F4F86A,
    0xC69F7B69, 0xD5CF889D, 0x27A40B9E, 0x79B737BA, 0x8BDCB4B9,
    0x988C474D, 0x6AE7C44E, 0xBE2DA0A5, 0x4C4623A6, 0x5F16D052,
    0xAD7D5351
)


def add(crc, buf):
    byte_buf = array.array('B', buf)
    for b in byte_buf:
        crc = (crc >> 8) ^ crc32c_table[(crc ^ b) & 0xff]
    return crc


def done(crc):
    tmp = ~crc & 0xffffffff
    b0 = tmp & 0xff
    b1 = (tmp >> 8) & 0xff
    b2 = (tmp >> 16) & 0xff
    b3 = (tmp >> 24) & 0xff
    crc = (b0 << 24) | (b1 << 16) | (b2 << 8) | b3
    return crc


def cksum(buf):
    """Return computed CRC-32c checksum."""
    return done(add(0xffffffff, buf))


def test_crc32c():

    def bswap32(x):
        from struct import pack, unpack
        return unpack('<I', pack('>I', x))[0]

    # reference test value from CRC catalogue
    # http://reveng.sourceforge.net/crc-catalogue/17plus.htm#crc.cat.crc-32c
    # SCTP uses tranport-level mirrored byte ordering, so we bswap32

    assert cksum(b'') == 0
    assert cksum(b'123456789') == bswap32(0xe3069283)
